Water turbine runner

ABSTRACT

A water turbine runner comprising a plurality of blades coaxially fixed to one axis each of said blades is composed of an iron-based material, wherein each blade is provided with a smooth surface weld metal on the surface where erosion due to cavitation liable to take place, said weld metal being made of an erosionresistant metal consisting essentially of up to 0.5 wt% of C, 10 to 30 wt% of Cr, 0.5 to 30 wt% of Co, up to 1 wt% of Si, up to 3 wt% of Mn, and the balance of Fe.

United States Patent 1191 Watanabe et al.

[ WATER TURBINE RUNNER [75] Inventors: Kiyoshi Watanabe; Kazuei Saito;

Tadaaki Kobayashi, all of Hitachi, Japan [73] Assignee: Hitachi, Ltd.,Tokyo, Japan [22] Filed: Apr. 28, 1972 [21] Appl. No.: 248,681

. Related US. Application Data [63] Continuation-impart of Ser. No.84,524, Oct. 27,

1970, abandoned.

[30] Foreign Application Priority Data Oct. 31, 1969 Japan 44-86833 [52]US. Cl. 416/241 [51] Int. Cl. F01d 5/28 [58] Field of Search416/186,-213, 241, 224

[56] References Cited UNITED STATES PATENTS 1.150.113 8/1915 Haynes75/126H 1,357,549 11/1920 Fahrenwald 75/126 H 2,201,425 5/1940 Berglund75/126 H [11] 3,794,445 1451 Feb. 26, 1974 2,272,534 2/1942 Trantlin75/126 H 2,624,671 1/1953 Binder et al. 75/126 H 3,293,030 12/1966 Childet a1. 416/224 UX 3,561,886 2/1971 Kreischer et al... 416/224 3,564,6892/1971 Hirtenlechnerl... 416/224 3,650,845 3/1972 Oda et al. 416/241 UX3,661,658 5/1972 Oda et al. 416/213 UX FOREIGN PATENTS OR APPLICATIONS728,972 4/1955 Great Britain 416/224 Primary EXaminerEverette A. Powell,Jr. Attorney, Agent, or Firm-Craig and Antonelli 57 ABSTRACT 21 Claims,1 Drawing Figure WATER TURBINE RUNNER CROSS-REFERENCE TOTHE RELATEDAPPLICATION This is a continuation-in-part application of the US. Ser.No. 84,524 filed on Oct. 27, 1970 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to a novel water turbine runner of which each blade is providedwith on the surface which is liable to undergo erosion due to cavitationa weldmetal high in resistance to erosion.

2. Description of the Prior Art A water turbine runner has a pluralityof blades coaxially fixed to one axis with which high speed watercollides to rotate the runner.

It is necessary that the runner is composed of a material capable ofwithstanding the power of rotation. Further, at the time when theoperation of a water turbine runner is discontinued, a power ofcounteraction is applied thereto, so that the runner should be composedof a material capable of withstanding the, power of counteraction. Forthe above reasons, a water turbine runner material should have a yieldstrength of at least 50 kg/mm an elongation of at least 20% and animpact of at least 6 kg-m/cm in general. Further, a water turbine runnerundergoes corrosion due to contact with high speed water, so that therunner material is required to have good resistance to corrosion aswell.

It is well known that a steel containing about 13 wt% of chromium whichhas a tempered martensite structure satisfies the conditions requiredfor water runner material, and has been applied to many runners.However, the above-mentioned steel has had such drawback that when arunner composed of said steel is put in motion the surface of each bladeopposite to the surface, with which high speed water collides atsubstantially a right angle, is brought to a state low in pressure andcauses cavitation-erosion due to impact action of the water. It hastherefore been an ordinary practice that in most cases, a material highin resistance to cavitation-erosion is welded to portions eroded bycavitation. As the welding material, a steel containing about 18 wt% ofchromium and about 8 wt% of nickel has been used in most cases inconsideration of the affinity for the runner material. The above weldingmaterial, however, is not sufficiently been satisfactory in resistanceto cavitation-erosion.

In order to inhibit the cavitation-erosion, a material high in hardnessmay be used so that the runner manufactured can-withstand the impactaction of water. In this sense, a cobalt alloy called sterite is mostpreferable, there were some cases where the sterite was actually used.However, a weldmetal of sterite has such a structure that an eutecticstructure composed'of a cobalt solid solution containing tungsten andchromium and a cobalt-tungsten double carbide fills the boundariesbetween grains of said solid solution and dendrite, and has suchdrawback that cracks are formed at portions where said eutectic carbideis present.

SUMMARY OF THE INVENTION OBJECTS OF THE INVENTION A principal object ofthe present invention is to provide a novel water turbine runner bladewhich is liable to undergo erosion due to cavitation provided withformed a weldmetal high in resistance to cavitationerosion and free ofoccurrence of welding cracks.

Another object of the invention is to provide a water turbine runnerprovided with blades which are cavitation-erosion resistant as excellentas that of sterite.

DESCRIPTION OF THE INVENTION The water turbine runner of the presentinvention comprises a plurality of blades coaxially fixed to one axiswherein the blades are composed of an iron-base material, each of theblades which is liable to undergo erosion due to cavitation beingprovided with a smoothed-surface weld-metal of an erosion-resistance theweldmetal consisting essentially of up to 0.5 wt% of C, 10 to 30 wt%ofCr, 0.5 to 30 wt% ofCo, up to 1 wt% of Si, up to 3 wt% of Mn, and thebalance of Fe.

A weldmetal formed on the surface of each blade of a runner is desirablysuch that it is not only high in harness but also is work-hardened whenhigh speed water violently collides therewith during the operation ofthe runner. In this respect, a weldmetal of the abovementionedcomposition is preferable.

The runner material may be any material so far as it has a yieldstrength of at least 50 kglmm an elongation of at least 20% and animpact of at least 6 kg-m/cm and thus includes substantially all ofiron-based materials. More preferably, however, it is necessary to use amaterial which itself is high in resistance to cavitationerosion andwhich shows an erosion amount of less than 200 mg/2 hr in amagnetostriction type erosion test, eg a steel containing 1 l to 14 wt%of chromium is preferable.

Among the elements constituting the weldmetal, Co is the most importantelement. That is, due to the presence of C0, the weldmetal can bework-hardened and prevented from weld-cracking. The action of Co for theprevention of weld-cracking is such that S, which segregate to theboundary of grains at the time of coagulation of weldmetal to become acause for the cracking, can be fixed as CoS prior to the coagulation andremoved as a slag.

I The composition ranges of the weldmetal have been decied on the basisof many experimental results and are grounded on the following facts:

C: The presence of C is necessary to increase the hardness of theweldmetal and to enhance the weldmetal in resistance tocavitation-erosion. On the other hand, however, C promotes the formationof eutectic carbide to bring about a cause for weld-cracking.Accordingly, the amount of C is preferably up to 0.5 wt%, morepreferably from 0.15 to 0.45 wt%.

Cr: The presence of Cr increases the mechanical strength and corrosionresistance of the weldmetal.

This effect is clearly observed when the amount of Cr is more than 10wt%. It has been confirmed that if the amount of Cr is up to 10 wt%,weld cracks are formed at high temperatures. The larger the amount ofCr, the greater the strength of the weldmetal. If the amount of Cr isexcessively large, however, the weldmetal is degraded in ductility tofinally bring about cold-cracking. It has thus been found that the upperlimit of Cr is 30 wt%.

Co: The presence of Co is effective for enhancing the weldmetal inresistance to cavitation-erosion and in prevention of weld-cracking.This effect is clearly observed when the amount of Co is more than 0.5wt%. However, a saturation is attained when the amount of Co is 30 wt%.For economical reason, therefore, the upper limit of Co is 30 wt%.

Si: Si has effects of deoxidizing the weldmetal and inhibiting themigration of impurities into the weldmetal. However, the presence of Sipromotes weld-cracking, so that the amount thereof should not exceed 1wt%.

Mn: Mn gives the same effects as those of Si. If the amount of Mn isexcessively large, however, crystal grains are made coarse to degradethe weldmetal in ductility. Accordingly, the amount of Mn should notexceed 3 wt%.

In the weldmetal, P and S are contained as inevitable impurities. Theseelements not only greatly promote weld-cracking but also bring aboutdegradation in ductility of the weldmetal. Accordingly, the amounts ofsaid elements should be limited to amounts as small as possible.According to experiments carried out by the present inventors, it hasbeen found that in order to obtain a weldmetal high in reliability, theamount of each of P and S should be less than 0.03 wt%.

In many studies, the present inventors have confirmed that a weldmetalcontaining Cr and Co in a total amount of 26 wt% or more is far less indegree of erosion than that containing said elements in a total amountof less than 26 wt%, and that a weldmetal is more lowered in degree oferosion with increasing amount of Cu hich is additionally incorporatedtherein. The reason why a weld-metal is improved in cavitationerosionresistance is ascribable to the fact that Cu dissolves in the matrix tobring about the enhancement in corrosion resistance of the weldmetal,with the result that the weldmetal is improved in erosion resistanceaccordingly. The effect of Cu is observed when it is used in an amountof 1 wt% or more. Since Cu greatly promotes weld-cracking, however, theupper limit of Cu is 8 wt%. The inventors have further confirmed that aweldmetal containing Cu and Co in a total amount of 6 wt% or more is farlower in degree of erosion than that containing said elements in a totalamount of less than 6 wt%.

A weldmetal, welded onto the surfaces of portions of a water turbinerunner which are liable to undergo cavitation-erosion ought to be madesmooth on the surface by processing the surface of the weldmetal afterwelding. In the welding, the welded surface should be processed so thatthe thickness of the weldmetal becomes 3 to 7 mm. In case the thicknessof the weldmetal is less than 3 mm, the weldmetal is undesirablymigrated with elements from the runner material to make it impossible toattain the desired composition. The adoption of a thickness of more than7 mm, is uneconomical.

A water turbine runner undergoes cavitation-erosion at various portions,through the portions vary depending on the kind of the runner. A Peltontype water turbine runner undergoes cavitation-erosion at portions wherethe pressure becomes low due to the flow of high speed water when theportions are deformed by collision of the high speed water. A Francisand Capran type water turbine runners undergo cavitation-erosion atopposite sides of portions with which high speed water collides.Accordingly, each of the abovementioned water turbine runners should bewelded with the aforesaid weldmetal at least on the surfaces of saidportions.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective, partiallybroken away, view of a Francis type water mill runner embodying thepresent invention.

EXAMPLES EXAMPLE 1 25 Kinds of weldmetal having the compositions shownin Table 1 were individually formed on the surface of a steel platecomposed of 0.20 wt% of C, 0.35 wt% of Si, 0.50 wt% of Mn, 0.021 wt% ofP, 0.016 wt% of S, and the balance of Fe. At the time of preparation ofeach welding rod used, the amount of each of P and S had been socontrolled as to become less than 0.01 wt%. The welding rod was preparedby coating a flux on a core wire of 4 mm in diameter so that theresulting welding rod came to have a diameter of 6.25 mm. The weldingwas carried out under the same conditions as in the case where thewelding rod is actually welded to a water turbine runner. Concretely,the welding was conducted by the use of an alternating current weldingmachine, wherein the welding current was to A and the temperaturebetween strata was 150 to 200 C. In order to take up a sample from theresulting weldmetal, the thickness of the weldmetal was made 15 mm. Theflux used had been composed of 28 wt% of CaCO:,, 6 wt% of CaFe, 45 wt%of rutile, 2 wt% of mica, 3 wt% of Mn, 5 wt% of Fe-Ti, 1 wt% of K TiOand the balance of Na SiO TABLE 1 cswa i nfi Cr Co Si- Mn w Ni- Fe 10.13 9.4 12.9 0.21 0.37 Balance. 2 0.14 10.2 10.5 0.21 D0. 3 0.15 11.912.5 0.19 D0. 4 0.13 12.1 13.2 0.17 D0. 5 0.41 13.0 13.1 0.23 DO. 6..0.22 13.5 8.1 0.19 D0. 7 ..0.21 14.6 11.4 0.20 D0. 8 0.16 16.3 9.00.21 DO. 9 0.14 17.6 8.2 0.26 D6. 10..... 0.20 17.6 12.4 0.25 D0.11..... 0.27 18.1 12.6 0.18 D0. 12..... 0.24 20.1 6.0 0.20 D0. 13.....0.22 21.8 5.1 0.20 D0. 14..... 0.24 23.5 20.7 0.22 DO. 15..... 0.24 25.224.8 0.19 Do. 16..... 0.20 26.7 32.8 0.23 D0. 17..... 0.43 26.8 20.20.20 D0. 18..... 0.20 28.0 22.1 0.18 D0. 19..... 0.19 29.6 28.4 0.18 D6.20..... 0.40 29.8 0.8 0.20 D0. 21..... 0.31 31.8 28.4 0.25 D0. 22.....1.02 31.2 Balance 0.20 0.38 4.5 2.2. 0.06 7.7 0.31 0.60 6.92 8 161 66.24..... 0.08 18.5 0.58 0.77 8.15 D0.

Cracks were observed in the weldmetal Nos. 1 and 21, but no cracks wereobserved at all in the weldmetal Nos. 2 to 20. The crack ratio of eachof the weldmetal Nos. 1 and 21 was about 20% as measured according tothe Y type weld-cracking test regulated in JIS Z 3158. The stelliteweldmetal No. 22 formed many fine were as shown in Table 4.

cracks, and the crack ratio thereof according to the Y typeweld-cracking test was 100%.

Subsequently, an erosion test sample of 22 mm in diameter and mm inlength was taken up from each weld-metal, attached to a magnetostrictionvibration type erosion test apparatus and subjected 4 times to erosiontest for 30 minutes under such conditions as shown in Table 2. w

Erosion test conditions Frequency (KHz) 6.5 Amplitude (IL) 120 Testliquid Test temperature (C) State of test liquid Drinking water 25 18.11.6 3.3 0.31 0.50 Do. 18.2 2.2 5.6 0.28 1.12 Do. 18.4 5.8 2.1 0.19 1.40Do. 20.1 6.0 1.8 0.20 1.05 Do. 21.3 0.8 4.5 0.22 0.77 Do. 24.6 5.7 2.90.29 0.63 Do.

In the weldmetal No. 33, fine cracks were partly observed. This isascribable to the excessive amount of Cu. No cracks were observed in allother weldmetals than the weldmetal No. 33.

Subsequently, an erosion test sample of 22 mm in diameter and 10 mm inlength was taken up from each weld-metal, attached to a magnetostrictionvibration type erosion test apparatus, and subjected 4 times to erosiontest for 30 minutes under the same conditions It it well known that astellite weldmetal is minimum in amount of eroded portion. The sameresult was obtained in the above-mentioned test as well. Among theweldmetals according to the present invention, however, those which arelarger in amounts of Cr and Co are substantially equivalent incavitation-erosion resistance to stellite. The weldmetal No. 24 of asteel containing about 8 wt% of Ni and about 18 wt% of Cr, and theweldmetal No. 23 which is somewhat different in composition from thesaid weldmetal but has a stable austenite structure, like saidweldmetal, are markedly large in amount of eroded portions as comparedwith other weldmetals, and hence are not suitable for use ascavitation-erosion resistant weldmetals.

EXAMPLE 2 In the same manner as in Example 1, kinds of Cuincorporatedweldmetals are individually formed on a steel plate composed of 0.20 wt%of C, 0.35 wt% of Si, 0.50 wt% of Mn, 0.02 wt% of P, 0.016 wt% of S, andthe balance of Fe. The compositions of the weldmetals TABLE 4Composition (wt%) Stationary Tesllme (hr) 2 15 as in Example 1. In table3 are totalled the amounts of eroded portions In Table 5 are totalledthe amounts of eroded porefid @5130 minutes 31 351 1 9 every 39 elee...

TABLE 3 weldmetal No 1 2 3 4 5 6 7 s 9 10 11 12 Amount oferoded portions(mg/2 hr)... 14.1 12.0 10.0 9.0 3.3 11.2 6.8 8.8 7.8 5.1 3.2 7.0

" weldmetal No 13 14 15 16 17 1s 19 20 21 22 23 24 Amount of erodedportions (mg/2 hr) 6.5 3.5 3.2 2.05 2.1 2.5 2.0 5.2 2.0 2.0 26.7 82.5

TABLE 5 weldmetal No 25 26 27 28 29 30 31 32 33 34 35 36 37 28 39 Amountof eroded portions (mg/2 hr) 3.9 4.3 8.9 4.8 8.6 6.4 5.1 4.8 5.2 7.5 5.85.9 6.1 7.3 4.8

According to Table 5, the weldr'netal Nos. 27 and 29 are unexpectedlylarge in amount of eroded portions. If Cu is removed from the weldmetalNo. 29, the composition of said weldmetal is substantially the same asthat of the weldmetal No. 8. Accordingly, the amount of eroded portionsof the weldmetal No. 29 ought to be far smaller than that of theweldmetal No. 8. Nevertheless, the amount of eroded portions of theweldmetal No. 29 is merely 0.2 mg/2 hr smaller than that of theweldmetal No. 8. This is ascribable to the fact that the amount of Cu istoo small to display its effect. In view of its composition, theweld-metal No. 27 is considered to be comparable to a certain extent tothe weldmetal No. 31. Nevertheless, the amount of eroded portions of theweldmetal No. 27 is far larger than that of the weldmetal No. 31. Thisis also ascribable to the amount of Cu. Considering the facts that theweld-metal No. 31, which had been incorporated with 1.1 wt% of Cu,showed favorable erosion resistance and that fine cracks were observedin the weldmetal No. 33, the amount of Cu to be incorporated into aweldmetal is preferably from 1 to 8 wt%.

Thus, it has been confirmed that a weldmetal comprising up to 0.5 wt% ofC, 10 to 30 wt% of Cr, 0.5 to

30 wt% of Co, up to 1 wt% of Si, up to 3 wt% of Mn, and the balance ofFe and accompanying impurities is high in resistance tocavitation-erosion and forms no weld-cracks, and hence is best suitablefor welding to surfaces of portions of a water turbine runner of whichblades are liable to undergo cavitation-erosion.

FIG. 1 is a respective, partially broken away, view of a Francis typewater turbine runner. In the runner, the blades 10 have beenpress-molded with a predetermined radius of curvature, and the materialthereof is a steel containing about 13 wt% of chromium.

A cause for generation of cavitation is that the blades have a complexcurved surface, and another cause therefor is that the cavitation isclosely related with the surfaces of blades positioned at the down-flowside of the runner, i.e. with the side of handling 14. Moreparticularly, the blades have been so constructed that the angle of eachblade to the direction of water flow becomes greater as the blade isextended to the side of band ring 12. Further, the Francis type waterturbine runner is rotated due to the impact of water flow which isapplied to the blades 10 and due to the difference in pressure betweenthe up-flow side, which is chiefly formed on the side of band ring 12,and the down-flow side. Accordingly, it is inevitable that low pressureportions are formed on the down-flow side, and thus the cavitation isfrequently generated in said low pressure portions. The portions, inwhich the cavitation is generated, are concretely represented by theportion A in FIG. 1.

In another embodiment of the present invention, a weldmetal comprising0.24 wt% of C, 25.2 wt% of Cr, 24.8 wt% of Co, 0.19 wt% of Si, 0.36 wt%of Mn, and the balance of Fe was formed on the surfaces of portions of a29,000 kw Francis type water turbine runner.

,Concretely, the said portions corresponded to the portion A in FIG. 1.The water turbine runner was made of SUS 50HP, was composed of 0.09 wt%of C, 0.25 wt% of Si, 0.35 wt% of Mn, 0.025 wt% of P, 0.006 wt% of S,0.44 wt% of Ni, 1 1.71 wt% of Cr, and the balance of 'Fe, and had anaverage thickness of 50 mm. The welding was effected by the use of analternating current welding machine, wherein the welding current was I30to 150A, and both the preheating temperature and the temperature betweenstrata were 150 to 200 C. The diameter of welding rod core wire, thecomposition of flux, and the diameter of welding rod were the same asthose in Example I.

At portions of the water turbine runner to which the welding was to beapplied were previously formed recesses of 30 X 30 mm in area and 5 mmin depth, and the aforesaid weldmetal was welded in said recesses andthen cooled as it was to 150 C. Thereafter, the weldmetal was heated to400 C and then cooled gradually. The welded portions were ground with agrinder so that the surfaces thereof were levelled with adjacentsurfaces of the runner, and then finished with sandpaper.

It was considered that a water turbine runner could not be used if thedepths of portions eroded due to cavitation-erosion or due to ordinaryerosion became.20% of the thickness of the runner plate, and that thelife of a conventional SUS SOI-IP-made water turbine runner wasordinarily 1 year. However, the life of a water turbine runnermanufactured in the above-mentioned manner is 4 years and thus has beenmarkedly prolonged.

While a preferred embodiment of the present invention has been explainedin the above with respect to the case of Francis type water turbinerunner, it is needless to say that the present invention is successfullyapplicable to the runner blades of Pelton type and Capran type waterturbines.

In the case of Capran type water turbine runner, like in the case ofFrancis type water turbine runner, cavitation is generated on the sidesopposite to the blade sur faces to which the power of water is applied,and the thus generated cavitation becomes a cause for erosion,

Accordingly, the portions of Capran type water turbine runner which areto be subjected to welding are the same as in-the case of Francis typewater turbine runner.

In the case of Pelton type water turbine runner, the power of water isapplied to the inner surfaces of buckets. If indented portions areformed on the inner surfaces of buckets clue to gravel and sandaccompanied with the water, the said portions become causes for bringingabout cavitation-erosion. In the case of Pelton type water turbinerunner, therefore, on the inner surfaces of buckets is formed theweldmetal.

We claim:

1. A water turbine runner comprising a plurality of blades coaxiallyfixed to one axis, said blades being composed of an iron-base material,wherein each blade is provided with a smooth-surface weld metal formedonly on the surface at the position where erosion due to cavitationtakes place, said weld metal consisting essentially of 0.1 to 0.5 wt.%of C, 10m 30 wt.% of Cr, 0.5 to 30 wt.% of Co, an effective amount foreffecting deoxidation up to 1 wt.% of Si, an effective amount foreffecting deoxidation up to 3 wt.% of Mn and the balance of Fe.

2. The water turbine runner of claim 1, wherein said weld metal containsless than 0.03 wt.% of P and S as inevitable impurities.

3. The water turbine runner of claim 1, wherein said weld metal containsfrom 0.17 wt.% to 1 wt.% of Si.

4. The water turbine runner of claim 3, wherein said weld metal contains0.35 wt.% to 3 wt.% of Mn.

5. The water turbine runner of claim 1, wherein said weld metal containsCr and Co in a total amount less than 26 wt.%.

6. A Pelton type water turbine runner comprising a plurality of bucketscoaxially fixed to one axis, the bucket being composed of an iron-basematerial, each of said buckets being provided with a smoothed-surfaceweld metal formed only on the surface at the position where high speedwater collides therewith and erosion due to cavitation takes place, saidweld metal consisting essentially of 0.1 to 0.5 wt.% of C, 10 to 30 wt.%of Cr, 0.5 to 30 wt.% of Co, an effective amount for effectingdeoxidation up to 1 wt.% of Si; an effective amount for effectingdeoxidation up to 3 wt.% of Mn and the balance of Fe.

7. A Capron or Francis type water turbine runner comprising a pluralityof blades coaxially fixed to one axis, the blades being composed of aniron-base material, each blade to which the high speed water collidesbeing provided with a smoothed-surface weld metal only on a part of thesurface of the blade at which erosion due to cavitation takes place,said weld metal consisting essentially of 0.1 to 0.5 wt.% of C, l0 to 30wt.% of Cr, 0.5 to 30 wt.% of Co, an effective amount for effectingdeoxidation up to 1 wt.% of Si, an effective amount for effectingdeoxidation up to 3 wt.% of Mn and the balance of Fe.

8. A water turbine runner comprising a plurality of blades coaxiallyfixed to one axis, the blade being composed of an iron-base material,each of said blades being provided with smoothed-surface weld metal onlyon a part where cavitation erosion takes place, said weld metalconsisting essentially of 0.l to 0.5 wt.% of C, 10 to 30 wt.% of Cr, 0.5to 30 wt.% of Co, I to 8 wt.% of Cu., an effective amount for effectingdeoxidation up to 1 wt.% of Si, an effective amount for effectingdeoxidation up to 3 wt.% of Mn and the balance of Fe and accompanyingimpurities.

9. A water turbine runner comprising a plurality of blades coaxiallyfixed to one axis, the blades being composed of an iron-base material,each of said blades being provided with smoothed-surface weld metal on apart of surface where cavitation-erosion takes place, said weld metalhaving a thickness of 3 to 7 mm. and consisting essentially of 0.1 to0.5 wt.% of C, 10 to 30 wt.% of Cr, 0.5 to 30 wt.% of Co, an effectiveamount for effecting deoxidation up to 1 wt.% of Si, an effective amountfor effecting deoxidation up to 3 wt.% of Mn, and the balance of Fe andaccompanying impurities.

10. A water turbine runner comprising a plurality of blades coaxiallyfixed to one axis, the blades being composed of a steel containing 1 1to 14 wt.% of chromium, each of said blades being provided with a weldmetal on an only part of surface where cavitationerosion takes place,said weld metal consisting essentially of 0.1 to 0.5 wt.% of C, 10 to 30wt.% of Cr, 0.5 to 30 wt.% of Co, an effective amount for effectingdeoxidation up to 1 wt.% of Si, an effective amount for effectingdeoxidation up to 3 wt.% of Mn; and the balance of Fe and accompanyingimpurities.

11. The water turbine runner of claim 10, wherein said weld metal has athickness of 3 to 7 mm.

12. A water turbine runner comprising a plurality of blades coaxiallyfixed to one axis, said blades being composed of an iron-base material,wherein each blade is provided with a smooth-surface weld metal formedonly on the surface at the position where erosion due to cavitationtakes place, said weld metal consisting of 0.1 to 0.5 wt.% of C, 10 to30 wt.% of Cr, 0.5 to 30 wt.% of Co, an effective amount for effectingdeoxidation up to 1 wt.% of Si, an effective amount for effectingdeoxidation up to 3 wt.% of Mn and the balance of Fe and inevitableimpurities.

13. The water turbine runner of claim 12, wherein said weld metalcontains less than 0.03 wt.% of P and S as inevitable impurities.

14. The water turbine runner of claim 12, wherein said weld metalcontains from 0.17 wt.% to 1 wt.% of Si.

15. The water turbine runner of claim 14, wherein the weld metalcontains from 0.35 wt.% to 3 wt.% of Mn.

16. The water turbine runner of claim 12, wherein the weld metalcontains Cr and Co in a total amount less than 26 wt.%

17. A water turbine runner comprising a plurality of blades coaxiallyfixed to one axis, the blade being composed of an iron-base material,each of said blades being provided with smoothed-surface weld metal onlyon a part where cavitation erosion takes place, said weld metalconsisting of 0.1 to 0.5 wt.% of C, 10 to 30 wt.% of Cr, 0.5 to 30 wt.%of Co, 1 to 8 wt.% of Cu, an effective amount for effecting deoxidationup to 1 wt.% of Si, an effective amount for effecting deoxidation up to3 wt.% of Mn, and the balance of Fe and accompanying impurities.

18. The water turbine runner of claim 17, wherein said weld metalcontains less than 0.03 wt.% of P and S as accompanying impurities.

19. The water turbine runner of claim 17, wherein the weld metalcontains from 0.17 wt.% to 1 wt.% of Si.

20. The waterturbine runner of claim 19, wherein the weld metal containsfrom 0.35 wt.% to 3 wt.% of Mn.

21. The water turbine runner of claim 17, wherein said weld metalcontains Cr and Co in a total amount less than 26 wt.%.

2. The water turbine runner of claim 1, wherein said weld metal containsless than 0.03 wt.% of P and S as inevitable impurities.
 3. The waterturbine runner of claim 1, wherein said weld metal contains from 0.17wt.% to 1 wt.% of Si.
 4. The water turbine runner of claim 3, whereinsaid weld metal contains 0.35 wt.% to 3 wt.% of Mn.
 5. The water turbinerunner of claim 1, wherein said weld metal contains Cr and Co in a totalamount less than 26 wt.%.
 6. A Pelton type water turbine runnercomprising a plurality of buckets coaxially fixed to one axis, thebucket being composed of an iron-base material, each of said bucketsbeing provided with a smoothed-surface weld metal formed only on thesurface at the position where high speed water collides therewith anderosion due to cavitation takes place, said weld metal consistingessentially of 0.1 to 0.5 wt.% of C, 10 to 30 wt.% of Cr, 0.5 to 30 wt.%of Co, an effective amount for effecting deoxidation up to 1 wt.% of Si;an effective amount for effecting deoxidation up to 3 wt.% of Mn and thebalance of Fe.
 7. A Capron or Francis type water turbine runnercomprising a plurality of blades coaxially fixed to one axis, the bladesbeing composed of an iron-base material, each blade to which the highspeed water collides being provided with a smoothed-surface weld metalonly on a part of the surface of the blade at which erosion due tocavitation takes place, said weld metal consisting essentially of 0.1 to0.5 wt.% of C, 10 to 30 wt.% of Cr, 0.5 to 30 wt.% of Co, an effectiveamount for effecting deoxidation up to 1 wt.% of Si, an effective amountfor effecting deoxidation up to 3 wt.% of Mn and the balance of Fe.
 8. Awater turbine runner comprising a plurality of blades coaxially fixed toone axis, the blade being composed of an iron-base material, each ofsaid blades being provided with smoothed-surface weld metal only on apart where cavitation erosion takes place, said weld metal consistingessentially of 0.1 to 0.5 wt.% of C, 10 to 30 wt.% of Cr, 0.5 to 30 wt.%of Co, 1 to 8 wt.% of Cu., an effective amount for effecting deoxidationup to 1 wt.% of Si, an effective amount for effecting deoxidation up to3 wt.% of Mn and the balance of Fe and accompanying impurities.
 9. Awater turbine runner comprising a plurality of blades coaxially fixed toone axis, the blades being composed of an iron-base material, each ofsaid blades being provided with smoothed-surface weld metal on a part ofsurface where cavitation-erosion takes place, said weld metal having athickness of 3 to 7 mm. and consisting essentially of 0.1 to 0.5 wt.% ofC, 10 to 30 wt.% of Cr, 0.5 to 30 wt.% of Co, an effective amount foreffecting deoxidation up to 1 wt.% of Si, an effective amount foreffecting deoxidation up to 3 wt.% of Mn, and the balance of Fe andaccompanying impurities.
 10. A water turbine runner comprising aplurality of blades coaxially fixed to one axis, the blades beingcomposed of a steel containing 11 to 14 wt.% of chromium, each of saidblades being provided with a weld metal on an only part of surface wherecavitation-erosion takes place, said weld metal consisting essentiallyof 0.1 to 0.5 wt.% of C, 10 to 30 wt.% of Cr, 0.5 to 30 wt.% of Co, aneffective amount for effecting deoxidation up to 1 wt.% of Si, aneffective amount for effecting deoxidation up to 3 wt.% of Mn; and thebalance of Fe and accompanying impurities.
 11. The water turbine runnerof claim 10, wherein said weld metal has a thickness of 3 to 7 mm.
 12. Awater turbine runner comprising a plurality of blades coaxially fixed toone axis, said blades being composed of an iron-base material, whereineach blade is provided with a smooth-surface weld metal formed only onthe surface at the position where erosion due to cavitation takes place,said weld metal consisting of 0.1 to 0.5 wt.% of C, 10 to 30 wt.% of Cr,0.5 to 30 wt.% of Co, an effective amount for effecting deoxidation upto 1 wt.% of Si, an effective amount for effecting deoxidation up to 3wt.% of Mn and the balance of Fe and inevitable impurities.
 13. Thewater turbine runner of claim 12, wherein said weld metal contains lessthan 0.03 wt.% of P and S as inevitable impurities.
 14. The waterturbine runner of claim 12, wherein said weld metal contains from 0.17wt.% to 1 wt.% of Si.
 15. The water turbine runner of claim 14, whereinthe weld metal contains from 0.35 wt.% to 3 wt.% of Mn.
 16. The waterturbine runner of claim 12, wherein the weld metal contains Cr and Co ina total amount less than 26 wt.%
 17. A water turbine runner comprising aplurality of blades coaxially fixed to one axis, the blade beingcomposed of an iron-base material, each of said blades being providedwith smoothed-surface weld metal only on a part where cavitation erosiontakes place, said weld metal consisting of 0.1 to 0.5 wt.% of C, 10 to30 wt.% of Cr, 0.5 to 30 wt.% of Co, 1 to 8 wt.% of Cu, an effectiveamount for effecting deoxidation up to 1 wt.% of Si, an effective amountfor effecting deoxidation up to 3 wt.% of Mn, and the balance of Fe andaccompanying impurities.
 18. The water turbine runner of claim 17,wherein said weld metal contains less than 0.03 wt.% of P and S asaccompanying impurities.
 19. The water turbine runner of claim 17,wherein the weld metal contains from 0.17 wt.% to 1 wt.% of Si.
 20. Thewater turbine runner of claim 19, wherein the weld metal contains from0.35 wt.% to 3 wt.% of Mn.
 21. The water turbine runner of claim 17,wherein said weld metal contains Cr and Co in a total amount less than26 wt.%.